Electronic communications such as e-mail are being increasingly used for both business and personal uses. Electronic communications has many advantages over non-electronic communications such as postal mail. These advantages include low cost, rapid delivery, ease of storage, and so on. As a result of these advantages, there is also an important disadvantage of electronic communications: junk mail, spam, and other types of unwanted electronic communications. Because of its low cost and speed, many organizations use electronic communications to advertise. For example, a mortgage company may purchase a list of e-mail addresses and send an e-mail message containing an advertisement for the mortgage company to each e-mail address. It is not uncommon for a person to receive many such unwanted and unsolicited e-mail messages a day. People receiving such junk e-mail messages typically find them annoying. Junk e-mail messages may also cause a person's inbox to become full and may make it difficult to locate and identify non-junk e-mail messages.
Various techniques have been developed to combat junk e-mail. For example, some e-mail systems allow a user to create a list of junk e-mail senders. When an e-mail message is received from a sender on the list of junk e-mail senders, the e-mail system may automatically delete the junk e-mail message or may automatically store the junk e-mail message in a special folder. When a junk e-mail message is received from a sender who is not currently on the junk e-mail list, the recipient can indicate to add that sender to the list. As another example, some e-mail systems may allow the recipient to specify a list of non-junk senders. If an e-mail message is received from a sender who is not on the list of non-junk senders, then the e-mail system may automatically delete or otherwise specially handle such an e-mail message.
A disadvantage of these techniques for combating junk e-mail is that the recipients are responsible for specifying who is a junk sender and a non-junk sender. It would be desirable to have a technique for combating junk e-mail that relieves the recipient of such responsibility.